Multimolecular Forms of Pyruvate Kinase from Rat and Other Mammalian Tissues

I. Electrophoretic Studies

抄録

It was established that the M types of pyruvate kinase (PK) [EC 2. 7. 1. 40] in muscle and liver differed electrophoretically, the enzyme in muscle migrating rather faster than that in liver. Therefore, these enzymes were tentatively designated as M₁ (skeletal muscle type-M) and M₂ (liver type M), respectively. In rats, the M₂-type is widely distributed in glycolytic tissues, such as liver, kidney, brain, heart, thymus, spleen, lung, adipose tissue, testis, ovary, ascites hepatoma AH-130, Walker's tumor, tumors induced by 3'-Me-DAB and cultured cells originating from hepatic cells. The M₁-type is present in muscle as the only component, and in brain as the major com-ponent. The L-type is present in liver as the major component and in kidney as a minor component. Thus the M₁- and L-types are only present in a few tissues with specialized physiological functions. Three unique forms of PK, M₁-, M₂-, and L-type, were also found in mouse and human tissues.
The electrophoretic patterns of the PK isozymes from rat tissues change greatly during differentiation and dedifferentiation. That is, the M₂-type is predominant in fetal muscle, brain and liver, but during differentiation from the fetus to the adult, (1) the M₂-type disappears and the M₁-type becomes predominant in skeletal muscle, (2) the M₂-type decreases and the L-type increases and becomes predominant in liver and (3) the M₂-type decreases and the M₁-type becomes predominant in brain. In contrast, in non cancerous portions of the liver of cancer-bearing animals, the L-type decreases, and the M₂-type increases and becomes predominant with increased growth of the cancer, and the isozyme pattern finally changes to that of cancer cells where the M₂-type is the only component. Furthermore, no PK specific for cancer cells could be detected. These results, therefore, strongly suggest that M₂-type PK is the prototype of the PK isozymes, while the L- and M₁-types are differentiated types.
PK in erythrocytes (R. B. C. -PK) differs electrophoretically from the M₁-, M₂-and L-types, separating from them and moving toward the anode rather slower than the L-type.